MOUTH PARTS OF THE PAL/EMONID PRAWNS. 



63 



ends in a semicircular surface, which bears a comma-shaped patch 

 of serrated ridges. Sollaud, who called attention to the difference 

 between the molar surfaces of Desmocaris and those of other 

 Pahemonidse *, pointed out that these ridges also occur in the 

 Acanthephyridae, and regarded them as a primitive feature. In 

 this he is probably right, since, as I have shown, a similar 

 arrangement is found in Nebalia and certain Branchiopoda. In 

 Amphibetceus and some Hippolytidae (text-fig. 43) part of the 

 surface is covered with such ridges and part with bristles, and 

 lobes of various shapes are appearing. We have here probably a 

 transition from the ridged condition to that which is found, for 

 instance, in Pontoniina?. 



Text-figure 44. 



Text-figure 45. 



Text-fig. 44. — Ventral view of mouth-parts of Leander serratus after removal 



of maxillipeds, maxillae, and left maxillule. 

 Text-fig. 45. — The same after removal of maxillules and paragnatha. 



For lettering see p. 71. 



2. The mandibles lie (text-figs. 44, 45) in a chamber enclosed 

 between the lips, the hood-like labrum standing in front of them, 

 and the large bilobed metastoma behind, while the swollen bases 

 of the mandibles themselves close in the chamber at the sides. 



* C. R. Ac. Sci. clii. p. 913 (1911). 



